Heat pipe suitable for application in electronic device with limited mounting space

ABSTRACT

A mesh-type heat pipe ( 10 ) includes a casing ( 12 ), a tube ( 14 ) located inside the casing and a screen mesh wick ( 16 ) located between the casing and the tube. The tube defines therein a plurality of through holes ( 142 ) and at least one cutout ( 144 ). The wick is held against the casing by the tube. Under the support of the tube, the wick as a whole engages closely an inner surface of the casing, thereby establishing an effective heat transfer path between the casing and a working fluid that is saturated in the wick. Meanwhile, with the cutout in the tube presented, the heat pipe incorporating such tube is easily to be bent or flattened so as to enable the heat pipe to be applicable in electronic devices with a limited mounting space for a cooling device, such as notebook computers.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for transfer ordissipation of heat from heat-generating components such as electroniccomponents, and more particularly to a heat pipe that is suitable foruse in electronic devices that have a limited mounting space, such asnotebook computers.

DESCRIPTION OF RELATED ART

Heat pipes have excellent heat transfer performance due to their lowthermal resistance, and therefore are an effective means for transfer ordissipation of heat from heat sources. Currently, heat pipes are widelyused for removing heat from heat-generating components such as centralprocessing units (CPUs) of computers. A heat pipe is usually a vacuumcasing containing therein a working fluid, which is employed to carry,under phase transitions between liquid state and vapor state, thermalenergy from one section of the heat pipe (typically referring to as“evaporating section”) to another section thereof (typically referringto as “condensing section”). Preferably, a wick structure is providedinside the heat pipe, lining an inner wall of the casing, for drawingthe working fluid back to the evaporating section after it is condensedat the condensing section. Specifically, as the evaporating section ofthe heat pipe is maintained in thermal contact with a heat-generatingcomponent, the working fluid contained at the evaporating sectionabsorbs heat generated by the heat-generating component and then turnsinto vapor. Due to the difference of vapor pressure between the twosections of the heat pipe, the generated vapor moves towards and carriesthe heat simultaneously to the condensing section where the vapor iscondensed into liquid after releasing the heat into ambient environmentby, for example, fins thermally contacting the condensing section. Dueto the difference of capillary pressure developed by the wick structurebetween the two sections, the condensed liquid is then drawn back by thewick structure to the evaporating section where it is again availablefor evaporation.

The wick structure currently available for the heat pipe includes finegrooves integrally formed at the inner wall of the casing, screen meshor bundles of fiber inserted into the casing and held against the innerwall thereof, or sintered powder combined to the inner wall of thecasing by sintering process. As for the screen mesh wick, itsmanufacture generally involves weaving together a plurality of pliablewires or threads such as metal wires or synthetic fibers. In this sense,the screen mesh wick is formed separately and is then inserted into thecasing of the heat pipe.

In the heat pipe, except the function to generate capillary force fordrawing the condensed liquid back to the evaporating section of the heatpipe, another function of the wick structure is to provide a heattransfer path between the casing of the heat pipe and the working fluidthat is contained in the casing and saturated in the wick structure.Therefore, whether the wick is maintained into intimate contact with thecasing will have a great impact on the heat transfer effect of the heatpipe. However, since the screen mesh wick is made separately, in manycases a gap will exist between the screen mesh wick and the casing ofthe heat pipe after the screen mesh wick is inserted into the heat pipe.In order to hold the screen mesh wick against and ultimately into closecontact with the casing of the heat pipe, retaining means are oftenused. For example, a helical spring or a round tube will generally servethis purpose. The helical spring is not satisfactory in holding thescreen mesh wick against the casing of heat pipe since it generallycannot apply a uniform force on the wick for pressing it against thecasing due to a limited contact area between the spring and the wick.

In many cases, a heat pipe is required to be bent into a curved one orpressed into a flattened one in order to be applicable in electronicdevices that have very limited mounting space, for example, in someportable electronic devices such as notebook computers. Although theround tube could provide a more uniform pressing force for the wick incomparison to the helical spring, the tube generally is made of rigidmaterial such as metals and therefore adds difficulty to the bending orflattening work, since the rigidity of the tube has to be overcome inorder to bend or flatten the heat pipe.

Therefore, it is desirable to provide a retaining means for the screenmesh wick that could apply a uniform pressing force for the wick andmeantime make the bending or flattening work to the heat pipe, ifnecessary, more easier.

SUMMARY OF INVENTION

A heat pipe in accordance with one embodiment of the present inventionincludes a casing, a tube located inside the casing and a screen meshwick located between the casing and the tube. The tube defines therein aplurality of through holes and at least one cutout. The wick is heldagainst the casing by the tube. Under the support of the tube, the wickas a whole engages closely an inner surface of the casing, therebyestablishing an effective heat transfer path between the casing and aworking fluid that is saturated in the wick. Meanwhile, with the cutoutin the tube presented, the heat pipe incorporating such tube is easilyto be bent or flattened so as to enable the heat pipe to be applicablein electronic devices with limited mounting space for cooling device,such as notebook computers.

Other advantages and novel features of the present invention will becomemore apparent from the following detailed description of preferredembodiment when taken in conjunction with the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a heat pipe inaccordance with a first embodiment of the present invention;

FIG. 2 is an isometric view of the heat pipe of FIG. 1, showing variousparts thereof in the assembly process;

FIG. 3 is a side elevation view of a tube suitable for the heat pipe ofFIG. 1, according to a second embodiment of the present invention;

FIG. 4 is a side elevation view of a tube suitable for the heat pipe ofFIG. 1, according to a third embodiment of the present invention; and

FIG. 5 is a cross-sectional view of the tube of FIG. 4, taken along lineV-V thereof.

DETAILED DESCRIPTION

FIG. 1 illustrates a heat pipe 10 in accordance with one embodiment ofthe present invention. The heat pipe 10 includes a casing 12, a tube 14inserted into the casing 12 and a capillary wick 16 located between thecasing 12 and the tube 14. The wick 16 is held by the tube 14 to engageclosely an inner surface of the casing 12. The casing 12 is typicallymade of high thermally conductive materials such as copper or copperalloys. Although the casing 12 as illustrated is in a round shape, itshould be recognized that other shapes, such as rectangle or the like,may also be suitable. The wick 16 is a screen mesh wick having a porousstructure and is saturated with a working fluid (not shown), which actsas a heat carrier for carry thermal energy inside the heat pipe 10 whenundergoing a phase transition from liquid state to vaporous state. Theworking fluid is usually selected from liquids such as water or alcoholand is compatible with the wick 16, the tube 14 and the casing 12.

The screen mesh wick 16 is typically made independently of the casing 12by weaving together a plurality of flexible wires or threads such asmetal wires or synthetic fibers. Then the wick 16 is rolled and insertedinto the casing 12. The tube 14 is capable of applying a uniformpressing force on the wick 16 in order to maintain the wick 16 as awhole into close contact with the casing 12, thus providing an effectiveheat transfer path between the casing 12 and the working fluid saturatedin the wick 16. The tube 14 defines therein a plurality of through holes142 through its inner and outer surfaces thereof. These through holes142 are round in shape, although other shapes such as rectangle ortriangle or the like may also be suitable. In addition, the throughholes 142 may be arranged at the tube 14 regularly or irregularly. Thedesign of the through holes 142 is to enable a communication of theworking fluid between the wick 16 and a hollow vapor channel (notlabeled) defined in the casing 12 and the tube 14. Specifically, whenthe working fluid contained in the wick 16 receives heat from a heatsource in thermal connection with an evaporating section (not labeled)of the heat pipe 10 and turns into vapor, the vapor goes into the vaporchannel defined by the casing 12 via the through holes 142 and thenmoves, through the vapor channel, toward a condensing section (notlabeled) of the heat pipe 10 where the vapor releases its heat and turnsinto liquid. Then, the condensed liquid returns from the vapor channelinto the wick 16 again via the through holes 142. Thereafter, the liquidis drawn back to the evaporating section of the heat pipe 10 via thewick 16 where it is available again for evaporation. The through holes142, preferably, account for about 70 percents of a total surface areaof the tube 14 so as to enable the vapor to go into the vapor channeland the liquid to return back the wick 16 smoothly. In this situation,however, the tube 14 is still capable of providing enough support forthe wick 16.

In order for the heat pipe 10 to be suitable for use in electronicdevices such as notebook computers where the heat pipe 10 is usuallyrequired to be in a curved or flattened configuration due to limitedmounting space inside these electronic devices, the tube 14 definestherein a cutout 144 along a circumferential direction thereof. Thecutout 144 is elongated. The cutout 144 extends through a large portionof a circumferential periphery of the tube 14, but does not cut the tube14 into two pieces. Due to the existence of the cutout 144, the heatpipe 10 is easily to be bent into a curved configuration from thelocation where the cutout 144 is located, without the necessity ofovercoming the rigidity of the tube 14 especially if the tube 14 is madeof rigid material such as metals. Although in this embodiment the cutout144 forms a right angle with respect to an axis (not labeled) of tube14, it should be recognized that in some other circumstances the cutout144 may also be defined slantwise in the tube 14 and in doing so, anacute angle is formed between the cutout 144 thus defined and the axisof the tube 14. It should also be recognized that if the heat pipe 10 isneeded to be bent in more than one location, more than one cutout 144may be formed in the tube 14. The tube 14 may be made of metals such ascopper or aluminum, and in order to reduce the rigidity of the tube 14,organic material such as polyethylene, polycarbonate, polyamide, or thelike may also be suitable for the tube 14.

As shown in FIG. 2, in assembly, the wick 16 which is typically made byweaving technology is firstly wrapped around on the tube 14. The tube 14may be manufactured by pressing or forging or injection molding to formfirstly a flat plate with the through holes 142 formed therein and thenrolling the flat plate into the tube 14. Then, the tube 14, togetherwith the wick 16 wrapped therearound, is inserted into the casing 12after the casing 12 is heated to expand with a required extent. As thecasing 12 is cooled down to its original size, the wick 16 is therebytightly and evenly held against the inner surface of the casing 12 underthe support of the tube 14.

FIG. 3 illustrates a tube 14 a according to a second embodiment of thepresent invention. Compared with the above-mentioned first embodiment,the tube 14 a is divided into two separate pieces by an elongated cutout145 transversely cutting through the tube 14 a.

FIGS. 4-5 illustrate a tube 14 b according to a third embodiment of thepresent invention. The tube 14 b defines therein a pair of oppositeelongate cutouts 146 along a longitudinal direction thereof. Each cutout146 has two sections (not labeled) extending from opposite ends of thetube 14 b till a middle thereof. The two sections do not communicatewith each other. In the presence of the cutouts 146, this tube 14 b istypically suitable for use in heat pipes that need to be pressed intoflattened configurations.

According to the above-mentioned embodiments, each of the tubes iscapable of providing a uniform pressing force against the wick of theheat pipe so as to maintain the wick into intimate contact with thecasing of the heat pipe, thereby establishing an effective heat transferpath between the casing and the working fluid saturated in the wick.Meanwhile, with the cutouts in the tubes presented, the heat pipesincorporating such tubes are easier to be bent or flattened in order tobe applicable in modern electronic devices having a limited mountingspace for a cooling device.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A heat pipe comprising: a casing; a tube located inside the casing, the tube defining therein a plurality of through holes and at least one cutout; and a screen mesh wick located between the casing and the tube and held by the tube against the casing.
 2. The heat pipe of claim 1, wherein the at least one cutout extends along one of circumferential and longitudinal directions of the tube.
 3. The heat pipe of claim 1, wherein the tube is divided into multiple separate pieces by the at least one cutout.
 4. The heat pipe of claim 1, wherein the tube is made of one of organic material and metal material.
 5. The heat pipe of claim 1, wherein the through holes account for 70 percent of a total surface area of the tube.
 6. The heat pipe of claim 1, wherein the screen mesh wick is made of a plurality of flexible wires by weaving technology.
 7. A method for manufacturing a heat pipe comprising steps of: providing a tube with a plurality of through holes and at least one cutout defined therein; wrapping a screen mesh wick onto an outer surface of the tube; and inserting the tube and the wick into a hollow casing.
 8. The method of claim 7, wherein the tube and the wick are inserted into said casing after said casing is heated to expand with a required extent.
 9. The method of claim 7, wherein the screen mesh wick is made of a plurality of flexible wires by weaving technology.
 10. The method of claim 7, wherein the at least one cutout is formed along one of circumferential and longitudinal directions of the tube.
 11. The method of claim 7, wherein the tube is made of one of organic material and metal material.
 12. A heat pipe for transferring heat from one section to another section thereof, comprising: a metal casing having an inner surface defining a hollow space therein; a screen mesh wick contacting the inner surface of the metal casing; and a tube received in the hollow space and pressing the wick against the inner surface of the metal casing, wherein the tube defines a plurality of holes therethrough and at least one elongated cutout therein.
 13. The heat pipe of claim 12, wherein the at least one cutout is defined in the tube along a circumferential direction thereof.
 14. The heat pipe of claim 13, wherein the at least one cutout extends all through the tube and divides the tube into two pieces.
 15. The heat pipe of claim 13, wherein the least one cutout is perpendicular to an axis of the tube.
 16. The heat pipe of claim 13, wherein the at least one cutout is slanted to an axis of the tube.
 17. The heat pipe of claim 12, wherein the at least one cutout is defined in the tube along a longitudinal direction thereof.
 18. The heat pipe of claim 17, wherein the at least one cutout comprises two sections extending from two opposite ends of the tube toward a middle thereof.
 19. The heat pipe claim 17, wherein the tube comprises an additional cutout extending along the longitudinal direction thereof and located opposite the at least one cutout.
 20. The heat pipe of claim 19, wherein each of the at least one cutout and the additional cutout comprises two sections extending from two opposite ends of the tube toward a middle thereof. 